Apparatus for flotation



April 20, 1965 E. R. VRABLIK 3,179,252

APPARATUS FOR FLOTATION Filed Jan. 6. 1961 I 2 Sheets-Sheet 1 FIG.

h I 1 INVENTOR.

, EDWARD R.VRABLIK m ATTORNEY April 20, 1965 E. R. VRABLIK 3,

APPARATUS FOR FLOTATION Filed Jan. 6. 1961 2 Sheets-Sheet 2 FIG. 2

INVENTOR.

EDWARD R.VRABL|K existing solids. place, many bubbles will rise unimpeded to the surface without contacting any solids whatsoever.

United States Patent "cc 3,179,252 APPARATUS FOR FLOTATION Edward R. Vrablik, Arlington Heights, 11]., assignor to The Eimco Corporation, Salt Lake City, Utah, a corporation of Delaware Filed Jan. 6, 1961, Ser. No. 81,145 1 Claim. (Cl. 210-120) This invention relates generally to flotation and in particular to so-called dissolved air flotation in which a gas, usually air, is dissolved in liquid to form a saturated or super-saturated solution, then is precipitated as bubbles and allowed to rise and carry with it solids or liquids with which the bubbles associate in suflicient quantities to render buoyant.

H As is well known, flotation principles apply to liquidliquid as Well as liquid-solid separations. Hence although the following discussion is based on liquid-solids work, it applies equally to liquid-liquid systems.

In general, flotation depends on the bringing together of solids to be floated and a sufiicient quantity of air bubbles to render the solids buoyant in the system. In prior practice the bubbles either associate with existing solids by adhesion or are trapped in the surface interstices of an existing irregular solid such as a floc.

These prior systems have in common the requirement that air bubbles contact, then associate and remain with At best this is haphazard: In thefirst Second, even though contact is made with a solid, there is a high probability that the bubble will not permanently adhere there- .to as the solids turn and rise. As a consequence, flotation as heretofore practiced has arelatively low efliciency, on the order of 40-50%,based on the total quantity of air employed and available solids to be floated.

It has long been known that flotation efficiency and economy can be markedly increased if ways and means were available to insure greater contact between air and solidsand provide a positive union therebetween.

Hence, the primary object of the present invention is the provision of Ways and means to increase air-solids contact and insure a positive union between the solids and an A. further object is the provision of Ways and means enabling a high concentration of dissolved air in the An important related object is the provision of ways i and means enabling a positive gas-solids union by absorpcipitate air as bubbles, land forming solid fiocs about such bubbles during and after air precipitation.

3,179,252 Patented Apr. 20, 1965 both dissolved air and feed enter the feedwell together and are in communication during flocculation; consequently conditions are specifically provided for building fiocs around air bubbles.

In this connection, formation of flocs around bubbles is enhanced by initiating flocculation concomitantly with air precipitation. In accordance with this feature, chemical addition and flocculation are at least partially carried out during the initial stage pressure release. a

In order that'the invention may be more readily understood-and carried into eiiech reference is made to the accompanying drawings which, together with their description, are oflered by way of example only and are not to be taken as limiting the invention, the scope of which is defined by the appended claim rather than any preceding description.

In the drawings; a a

FIG. 1 illustrates, in simplified form a system embodying the invention.

FIG. 2 is a sectional view of flotation apparatus embodying the invention, certain portions being shown in elevation for purposes of clarity.

The system illustrated in FIG. 1 includes a flotation tank 10 having a usual overflow launder 11, an internal concentric baflie 12 defining an inner flotation compartment 13 from which clarified liquid passes to discharge after underflowing the baffle 12 into and through an outer compartment 14. The unit is equipped with a scum removal chamber 16 into which floated material is raked 23 and anoverlying flocculation zone 24 equipped with pickets 26 mounted on arms 27 in turn attached to and rotatable with the central shaft 21. The flocculation zone is further defined byan annular wall 28.

Influent is supplied to the submerged feedwell 23 via a feed conduit 29 which is arranged for tangential feed introduction.

Influent is introduced to the system, from a suitable source not shown, through a conduit 31 into a holding or surge tank 32 from which the influent stream is drawn,

via conduit .33, to and through the pressurization and Pressurization and aeration are, in accordance with the invention, effected by a two-stage pump system in which the first stage pressurizes the stream, pressured air isinjected into the pressured stream and the resulting aerated stream is passed through the second pump to mix and further dissolve air while increasing pressure.

Air is precipitated from the stream by a controlled stepwise release of preseure thereon which is accomplished by the combined use of a pressure relief valve which effects a sudden release of the major portion of the pressure, say 90-95%, a confining conduit through which the stream passes while undergoing further pressure relief bywhich air is precipitated, therefrom and an open aeration system.

Pressurization is accomplished by a first pump 34 and a second pump 36 arranged in series and conveniently driven by a common motor .37. As noted, the feed is partially pressurized in the first pump thence passes through a conduit or other pressured fluid confining passage 38 into and through the second pump 36 for further pressurization whence it passes via a conduit 39 into an excess free-air removal tank41.

Air is introdueedby injection into the partially pressurized feed stream between the discharge side of the first pump and the suction side of the second pump. Such injection i accomplished by means of a suitable air compressor system 42 which feeds compressed air via a suitable pressure regulator 43, valve 44, l flow meter 46, solenoid valve 47 and check valve 48 into air injection line 49 which communicates with the conduit 38 carrying partially pressurized feed between. the. first. andsecend pumps. Normally, a' single air injection point is employed, but in some instances two or more injection points may be desired. 'In such a case, this may be accomplished by a valve 50 and suitable branch line.

' Injection of air under conditions of pressure andpump agitation results in saturation of the influent stream with so-called dissolved air. Additionally, there may, in unusual cases be undissolved air present which should be removed prior to flotation as it expands and rises too rapidly to be of'value in flotation. Free air release is accomplished by means of a special tank 41 which receives aerated feed adjacent the bottom of an outer annular compartment 51 defined by concentric baffle 52 extending upwardly from the bottom to terminate below the top.

Aerated feed enters the tank, passes upwardly through the annular compartment 51, over the baffle 52 thence downwardly through the inner compartment 53 to dis charge via a conduit 54.

During its passage through the tank, which requires from 30 to 60 seconds, free air is released and bled from the system by a pressure relief valve 56. It will be noted that the system remains under pressure even during passage through the free-air removal tank thus insuring retention of dissolved air in solution.

Upon leaving the tank, aerated feed, now devoid of free-air, passes through a pressure regulating valve 57 which is operated at a pressure drop suflicient to release the major portion of pressure on the liquid to thereby initiate precipitation of air bubbles.

. Liquid from the valve, now under reduced pressure, passes into and through feed conduit 29 to enter the feedwell.

During passage through the feed conduit and feedwell residual pressure is slowly released, air bubble formation increases and the bubbles rise upwardly through the floc forming zone 24.

nuclei for fiocs whereby air is positively united with solids to be floated.

Since both fiocs and bubbles are undergoing simultaneous formation, contact efliciency is greatly increased. In actual practice, contact efl'iciency has been as high as is normally in the range of 85% to 95% as compared to the previously discussed prior systems which usually range from 40% to 50% efficiency.

In connection with flocculation, the invention contemplates the addition of flocculating agents, if needed, to the aerated stream prior to its introduction into the feedwell.

In the illustrated embodiment, this is accomplished by a suitable chemical feeder pump '58 which forces a stream of fiocculant, such as an alum suspension, through line 59 and valves 61 into the pressured stream in feed conduit 29. This insures initiation of floc formation concomitantly with air precipitation and further enhances airsolid contact.

An alternate chemical dosing scheme is to injectchemicals into the pressured feed ahead of the tank 41 thus utilizing the tank for preconditioning to gain the benefit of additional reaction time. This is useful under special conditions where slowly acting chemicals are used and only small floc formation occurs under pressure so there will be no fouling of the pressure relief valve 57 with solids or breaking up of already formed flocs upon passage through the valve.

For proper operation, it is necessary that the system be stabilized at a relatively constant liquid throughput rate. However, in most installations, actual feed rates fluctuate widely; to compensate for this, there is provided a valved recycle line 63 leading from the final discharge conduit 64 to the surge tank 32. Automatic recycle control is attained by means of a suitable float valve arrangement 66.

A Suitable p 67 and drain conduit 68 are provided for tank cleanout.

During floc formation, bubbles and. individual solid particles combine, the bubbles acting as In FIG. 2 there is shown in greater detail a flotation unit embodying the invention. Since various parts are similar, like reference numerals are used to identify similar parts.

The apparatus shown comprises a tank 10 having an overflow launder 11, an internal concentric baffle 12 extending from above the liquid level to terminate therebelow above the tank bottom thus defining an internal separation or flotation zone 13 and an annular discharge zone 14. There is provided an upper scum removal chamber 16, skimmers 17, scum outlet 18, and skimmer support arms 19 rotatable with shaft 21 driven by a suitable mechanism 22. a

A submerged feedwell 23 and overlying flocculation zone 24 with rotating pickets 26 mounted on arms 27 are located in the tank bottom at the center. These feedwell and flocculation zones are defined by a common wall 28.

Feed is supplied tangentially to the feedwell by'conduit 29, such feed being first pressurized by pumps 34 and 36 connected in series by a conduit 38. Pressured air is admitted to the system via a valved conduit 49 and the pressured-aerated feed is introduced to the system through a pressure relief valve 57 and feed conduit 29. Chemicals are added to the feed after pressure relief via suitable valved conduits 59.

Flocs of combined air bubbles and solids commence formation in the feed conduit 29, continue formation in the feedwell while swirling around therein, and complete formation under the influence of gentle agitation in the flocculation zone.

Buoyant material rises to the top of the inner compartment 13 and is removed by skimming. Clarified liquid passes under annular baffle 12 to discharge via launder 11 and conduit 64.

In actual comparative operations on oil refinery waste, containing 200 ppm. oil was subjected to treatment for oil removal in accordance with the invention. The feed stream was partially pressurized to about 21 p.s.i. in the first pump, air at 38 p.s.i. was injected into the partially pressured stream and the resulting stream further pres- .surized in the second pump to about 40 p.s.i.g. Upon passing through the relief valve, the pressure was sharply reduced to about 2 p.s.i.g. and the residual pressure released as the stream passed into and through the feed conduit, feedwell and flotation zone. The resulting eifluent contained only 20 ppm. oil. In other words, an oil removal efliciency of Using the same feed material but injecting the same amount of air at substantially the same pressures directly into the system in the bottom of the flotation zone, resulted in an effluent containing -120 p.p.m. oil; or an oil removal efliciency of only about 5060% A similar test was conducted using a system similar to that of the invention, but having only a single stage feed pressurization pump. The results showed only about 50% oil removal. 7

In connection with pressurization air injection and pressure release, I have found that total pressures in the range from 35-45 p.s.i. are proper for most materials. The first stage pump should contribute slightly. more than one-half of this in order to relieve the load on the second pump which must handle not only the liquid flow, but also the injected air as well. Air should be injected at a pressure of 10 to 15 pounds above the first pump discharge pressure in order to insure proper mixing and avoid the air following the conduit walls with consequent reduction in mixing efliciency.

I claim: 7

Flotation apparatus comprising a tank having a bottom and upstanding marginal sidewalls, peripheral overflow means adjacent the top of said sidewalls, open top feed receiving means centrally located adjacent the bottom of the tank, said feed receiving means being defined by a partial wall extending upwardly from the tank bottom awaasa and terminating below the elevation of said peripheral overflow means, a flocculation zone overlying said feed receiving means and in communication therewith through said open top, said zone being defined by an extension of said partial wall that terminates at an elevation below said peripheral overflow means, an annular bafiie mounted concentrically inside said tank in spaced relationship to said sidewall and extending from an elevation above said peripheral overflow means to terminate above the tank bottom at an elevation below said peripheral overflow means, said bafile defining an inner flotation zone of size greater than and in overlying surrounding relationship to said feed receiving means and said flocculation zone, a source of feed, and means for dissolving flotation air in and precipitating it from said feed, said means comprising a conduit interconnecting said source of feed and said feed receiving means, first and second feed pressurizing pumps mounted in series in said conduit for sequentially increasing pressure on said feed, a pressure relief valve in said conduit between the second of said pumps and said feed receiving means, and means enabling injection of pressured air into said conduit between said first and second pumps.

References Cited in the file of this patent UNITED STATES PATENTS 1,334,734 Callow et al Mar. 23, 1920 2,289,112 Fischer July 7, 1942 2,624,704 Fischer et al. J an. 6, 1953 2,695,710 Gibbs Nov. 30, 1954 2,713,026 Kelley et a1. July 1'2, 1955 2,759,607 Boyd et' a1. Aug. 21, 1956 2,793,185 Albrektsson et al. May 21, 1957 FOREIGN PATENTS 697,245 Germany Oct. 9, 1940 1,192,181 France Apr. 20, 1959 OTHER REFERENCES Rohlich: Application of Air Flotation to Refinery Waste Waters, Ind. Eng. Chem, vol. 46, February 1954, pp. 304-308. 

